1. Field of the Invention
This invention relates to a non-aqueous electrolyte battery and to a battery pack.
2. Description of the Related Art
Studies are now being vigorously made on a non-aqueous electrolyte battery which is designed to be charged and discharged by the movement of lithium ion between a negative electrode and a positive electrode for the purpose of using the battery as a high-energy density battery.
The non-aqueous electrolyte battery is expected to be useful as a middle or large scale power source in addition to the utilization thereof as a power source for miniature electronic devices. When the battery is to be used as a middle or large scale power source, the battery is demanded to be long in useful life and excellent in durability.
In the non-aqueous electrolyte battery, lithium transition metal composite oxides have been employed for the positive electrode thereof and carbonaceous materials have been employed for the negative electrode thereof. As for the transition metal, Co, Mn, Ni are now used.
In recent years, a non-aqueous electrolyte battery used negative electrode active materials which are capable of exhibiting an enhanced electrical potential in absorbing/desorbing lithium as compared with carbonaceous materials has been developed and the studies thereof are now continued. Among the negative electrode active materials of this kind, spinel type lithium titanate is considered as promising in terms of enhancing the charge/discharge cycle characteristics since this material is substantially free from changes in volume on the occasion of charge/discharge reactions.
Meanwhile, as described in JP-A 10-247496 (KOKAI) and JP-A 2000-268822 (KOKAI), the Ramsdellite-type lithium titanate or anatase-type titanium oxide is capable of exhibiting a greater theoretical capacity as compared with spinel-type lithium titanate. However, since the volume of these negative electrode materials are subject to shrink or expand due to the charge/discharge reactions, the twisting or peeling of the negative electrode is caused to occur, resulting in the deterioration of charge/discharge cycle characteristics of battery.
Further, JP-A 11-283624 (KOKAI) discloses a negative electrode having an negative electrode layer, the layer comprising negative active materials containing spinel-type lithium titanate which is coexisted with Ramsdellite-type lithium titanate. However, the non-aqueous electrolyte battery having such negative electrode is not necessarily satisfactory in charge/discharge cycle characteristics.
A negative electrode active material which is capable of exhibiting an enhanced electrical potential in absorbing/desorbing lithium as compared with carbonaceous materials is large in theoretical capacity and excellent in electron conductivity and in ionic conductivity. However, some of such negative electrode active materials are caused to shrink or expand in volume due to the charge/discharge reactions. When the volume of negative electrode active material is shrunk or expanded due to the charge/discharge reactions, the twisting negative electrode or the peeling of the negative electrode layer from the current collector is caused to occur, resulting in the deterioration of charge/discharge cycle characteristics of battery.